1. Field of the Invention
The present invention relates to an anode and a lithium battery including the anode, and more particularly, to an anode capable of tolerating a change in volume of an anode active material and a lithium battery with improved cyclic properties including the same.
2. Description of the Related Art
Non-aqueous electrolyte secondary batteries that use anodes formed of lithium compounds have relatively high voltages and relatively high energy densities, and have therefore been actively studied. In particular, when interest in lithium as an anode material was developing, lithium metals with large battery capacities were studied. However, in a battery using lithium metal as an anode, a large amount of lithium dendrites can precipitate on the lithium surface when the battery is being charged so that charge/discharge efficiency decreases or the anode becomes short-circuited with a cathode. In addition, lithium by itself is unstable. That is, lithium is susceptible to heat and impacts due to its high reactivity, and is explosive. However, these disadvantages of lithium metal can be overcome by using a carbonaceous anode. A carbonaceous anode is not formed of a lithium metal. That is, in a carbonaceous anode, lithium ions intercalate into and/or deintercalate out of interfaces of crystals of a carbonaceous electrode during charging/discharging and/or during an oxidation/reduction reaction.
However, lithium batteries using carbonaceous anodes have relatively low battery capacities due to the porous structure of carbon. For example, in a case of graphite that has a relatively high crystallinity, a theoretical capacity of LiC6 is 372 mAh/g, while a theoretical capacity of lithium metal is 3860 mAh/g.
It is known that lithium alloys, such as Li—Al, Li—Pb, Li—Sn, and Li—Si, can have larger electric capacities than carbonaceous materials. When these alloys or metals are used alone, however, a precipitation of lithium dendrites may lead to a number of problems as discussed above. Accordingly, in order to increase electric capacity and prevent short-circuiting, these alloys can be appropriately mixed with a carbonaceous material.
However, the mixing of an alloy (or metal) and a carbonaceous material results in another problem. That is, the carbonaceous material and the metal have different volume expansion rates when being oxidized and reduced, and the metal reacts with an electrolyte. Particularly, during charging, lithium ions enter an anode. In this case, the entire volume of the anode increases, and thereby has a denser structure. Then, during discharging, lithium is released from the anode in the form of lithium ions, thereby reducing the volume of the anode material. Here, when the carbonaceous material and the metal contract, due to different expansion rates of the carbonaceous material and the metal, gaps can be formed between the carbonaceous material and the metal, thereby causing an electrical disconnection. As a result, electrons do not flow smoothly, and thus the efficiency of the battery decreases. In addition, during charging/discharging, the metal can react with an electrolyte, thereby reducing the lifespan of the electrolyte and thus reducing the lifespan and efficiency of the battery.